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Scan List Section 4-2
Creating the Scan List The way that a scan list is prepared varies with the allocation method as
shown below.
Note 1. Be sure to create a scan list before starting actual system operation.
2. It is still possible to communicate with Units (with the scan list disabled) if
a scan list is not created when fixed allocations areas 1 to 3 are used. This
may result in faulty operation because the Master Unit will communicate
with slaves even if they do not start up due to problems, such as equipment
failure if there is no a scan list.
Scan List Enabled and Scan List Disabled
The scan list must be made. The scan list modes are described here.
Scan List Enabled (Used
for Actual Operation)
Remote I/O communications are performed according to the registered scan
list and only with slaves that are on the list. A verification error occurs (word
n+12, bit 00 in the status area turns ON) if a slave registered on the scan list is
not present on the network, if a slave did not start up when remote I/O com-
munications started, or if the number of I/O points did not match the number
registered.
Scan List Disabled (Used
when Changing System
Components)
Remote I/O communications can be performed with fixed allocations instead
of a scan list in order to change a system component. Do not operate without
a scan list during actual system operation. Use this mode only to replace a
Master Unit or to change a system component (change a connected slave or
a node address).
Note a) To disable the scan list, turn ON the Scan List Clear Switch (word
n, bit 01) during remote I/O communications with the scan list en-
abled (with fixed allocations, user-set allocations using allocated
DM Area words, or user-set allocations using the Configurator). In
all these cases, remote I/O communications are executed using
the fixed allocations area that was last used when the list was dis-
abled. All slaves are targeted for remote I/O communications with
the scan list disabled.
b) Slaves that are connected to the network while communications
are in progress are also targeted for communications. Errors can-
not be confirmed, however, even if there are slaves present that
did start up due to problems such as equipment failure because
there is no scan list available to check communications against.
The communications cycle time will also be significantly longer
than the calculated value.
c) The scan list is automatically enabled when user-set allocations
are set using the allocated DM Area words or the Configurator. If
the list is subsequently cleared using a software switch, fixed allo-
cations (1 to 3) will be used for remote I/O communications when
the scan list is disabled. Make sure the system has stopped before
Fixed allocations User-set allocations
through the allocated DM
Area words area
User-set allocations
through the Configurator
With the CPU Unit in PRO-
GRAM mode:
1. Turn ON the one of the
Master Fixed Allocation
Setting 1 Switches (1 to
3).
2. Turn ON the Scan List
Enable Switch.
With the CPU Unit in PRO-
GRAM mode, turn ON the
Master User Allocations
Setup Switch.
Create a list from the Con-
figurator. (Acquire a list of
online devices, use it to
create a scan list, and then
register the scan list in the
Master Unit.)